1. Field of the Invention
The present invention relates generally to a system and method of treating wastewater to produce a chemically acceptable effluent stream and more particularly to an automated system and method for treating wastewater that controls contaminant levels of a plurality of contaminants present in the wastewater while simultaneously minimizing chemical treatment costs and monetary fines imposed due to the release of substandard effluent into a municipal sewage system.
2. Description of the Related Art
The treatment of industrial wastewater is a necessary and difficult task common to most, if not all manufacturing facilities. A vast array of contaminants that are byproducts of manufacturing processes may be removed from the process by a wastewater stream. Accordingly, this wastewater stream carries contaminants in the form of suspended solids that range widely in size, as well as an assortment of liquids-oils, surfactants, polymers, acids, fats, blood, process ingredients, metal salts, total suspended solids (TSS), biological oxygen demand (BOD), chemical oxygen demand (COD) and the like. It is therefore necessary—in fact required—to remove and/or neutralize these contaminants to maintain an effluent stream that meets the minimum standards of wastewater sewage for a given locale prior to releasing the effluent into a sewage system.
As an added incentive, many municipalities levy fines for the discharge of effluents that do not meet their minimum standards, thereby potentially greatly increasing the cost of doing business. This problem is particularly acute where an effluent stream is highly variable, since it is difficult to maintain effluent stream contamination standards when the incoming wastewater stream varies greatly in its contaminant levels.
A variety of prior art systems for wastewater treatment employing various technical approaches have attempted to solve these problems. Systems employing tanks and weirs for separation of contaminants from liquids through sedimentation have been in widespread use. Sedimentation in holding tanks is often accompanied by utilizing filtration systems such as filters or screens to remove small solid particles in the effluent stream. However, filtration systems require a great deal of maintenance and are subject to clogging or partial clogging, thereby impeding flow through a system.
Dissolved air flotation systems (DAF's) have been employed with some degree of success wherein air bubbles are introduced at a lower portion of a dissolved it flotation tank to carry particles suspended in the liquid to the surface thereof. The solids at the surface aggregate together, either naturally or through the use of coagulant additives, thereby permitting removal of at least a portion of the solids in the wastewater. Effluent is then drawn from a lower portion of the DAF system. Furthermore, a variety of flotation systems are used where the solids being removed have densities close to that of water.
DAF systems vary widely in the time required to process a given wastewater stream depending upon the flow rate, contaminant levels, residence time of air bubbles in the DAF tank, the turbulence of the liquid stream being introduced to the DAF tank, DAF tank size, and the presence of more than one wastewater stream entering a tank. Due to the unpredictable nature of these variables there may be a considerable time lag between introduction of treatment chemicals into the wastewater stream and acceptable effluent contamination levels at the outlet of the DAF. This difficulty is further enhanced by widely varying contaminant levels in wastewater streams.
Many wastewater solids may include charged particles-oils, greases, fats, and other emulsified particles. Treatment of these types of contaminants often includes the use of coagulant and flocculant chemical additives to produce colloidal particles, termed “flocs” which can then be skimmed and removed. However, the use of coagulants and flocculants for neutralizing these contaminants must be carefully monitored because in too great a quantity, the flocs tend to break apart as they once again acquire a charge. In this situation, the wastewater treatment chemicals have been utterly wasted, and the wastewater must be re-treated before release into an effluent stream or be discharged as non-compliant wastewater.
Additionally, in many wastewater systems the pH of the wastewater stream must be modified to an acceptable level by the addition of cationic or anionic chemicals into the wastewater stream, and frequent testing of pH levels of the effluent to maintain proper pH balance.
In order to properly balance the chemical additives required to treat a contaminated wastewater stream, plant operators typically conduct “jar” tests wherein a plurality of jars or containers are filled from the wastewater stream, and each is treated with a differing chemical additive, or alternatively a combination of chemical additives, in differing amounts. When multiple additives such as coagulants and polymers are required to treat the wastewater, a plurality of jar tests are required to test various combinations of additive amounts to determine which combination results in an effluent that is acceptable for discharge from the system.
The requisite amount of chemical additives necessary to treat the wastewater are then recorded, and the flow rate of each additive must then be calculated based upon the rate of flow of wastewater into the treatment system. Once the proper flow rates are established the chemical additives are typically supplied to the system by pumps, which must be set to deliver the proper additive flows.
One great difficulty of this system of wastewater treatment is that if the wastewater input stream changes appreciably, the additives must be readjusted, thereby requiring additional jar tests. Additionally, a change in wastewater stream flow requires the pumps to be adjusted, since the proportion of additives must be adjusted proportionally to the wastewater stream flow. Furthermore, in many manufacturing environments it is impractical to train personnel to monitor the effluent stream, conduct periodic and frequent jar tests, calculate additive flow rates, make pump adjustments, and carefully monitor incoming stream flow rates in order to maintain the treatment system's operation.
Accordingly, there is a need for an automated wastewater treatment system that is capable of monitoring an effluent stream for out of range contaminant levels, conducting jar tests, and adjusting additive flow rates accordingly.